Assembly of stacked elements and method of producing the same

ABSTRACT

In an assembly in which a space between two elements is filled with a filler containing resin, a configuration that can limit both the size of the assembly and the cost of the fillers is provided. 
     Assembly  10  of stacked elements has: first element  2  having first surface  21 ; resin layer  61  that is arranged on first surface  21  and that contains a plurality of fillers F; and second element  4  that is arranged on resin layer  61  and that has second surface  41  that is in contact with resin layer  61 . In a section that is perpendicular to second surface  41 , the average flattening ratio of fillers F 2  that are in contact with second surface  41  is larger than the average flattening ratio of fillers F 1 , F 3  that are not in contact with second surface  41 . Here, the flattening ratio is a ratio of the maximum length of the filler in a direction parallel to second surface  41  to the maximum thickness of the filler in a direction perpendicular to second surface  41.

BACKGROUND OF THE INVENTION Field of the Invention

The present application is based on and claims priority fromJP2019-042832, filed on Mar. 8, 2019, the disclosure of which is herebyincorporated by reference herein in its entirety.

The present invention relates to an assembly of stacked elements and asensor package, as well as methods of manufacturing these, particularlyto the configuration of fillers of a sealing resin.

Description of the Related Art

Conventionally, a package is known in which an electric component, suchas a sensor unit, is connected to another electric component and inwhich these components are entirely sealed with resin. Such a package isused to connect many external connection terminals to an electriccomponent of a small size. A package in which external connectionterminals protrude beyond the electric component is also called afan-out package.

A filler containing resin is used as the resin. A filler containingresin is resin, such as epoxy resin, mixed with fillers that are made ofinorganic material, such as silica. In general, resin has a highcoefficient of thermal expansion when it cures, and the resin that hascured causes large stress, which may in turns functionally affect theelectric component. Due to a low coefficient of thermal expansion offillers, as compared to resin, the coefficient of thermal expansion of afiller containing resin is lower than that of resin that does notcontain fillers, and the above-mentioned problem is less likely tooccur.

In order to limit the size of a package, it is preferable that aconnection between electric components be as compact as possible. Forexample, when two electric components are connected via an extractionelectrode, a gap having the same dimension as the thickness of theextraction electrode may be formed between the two electric components.The gap is also filled with resin. However, since it is preferable thatthe gap be as small as possible, fillers having small diameters are usedfor the filler containing resin. JP2014-56924 discloses resin thatcontains filler whose maximum diameter is 5 μm.

SUMMARY OF THE INVENTION

The cost of fillers is correlated to the diameter of the fillers, and,in general, the cost of fillers having small diameters is high.Accordingly, when a small gap is filled with a filler containing resin,the cost of the fillers may increase. If the gap is large, then the costof the fillers can be limited because the large gap can accommodatefillers having large diameters, but it is difficult to limit the size ofa package. This problem occurs when a gap between electric components isfilled with a filler containing resin, but also generally occurs when aspace between two elements is filled with a filler containing resin.

The present invention relates to an assembly in which a space betweentwo elements is filled with a filler containing resin and aims atproviding a configuration that can limit both the size of the assemblyand the cost of the fillers, as well as a method of manufacturing suchan assembly.

An assembly of stacked elements according to the invention comprises: afirst element having a first surface; a resin layer that is arranged onthe first surface and that contains a plurality of fillers; and a secondelement that is arranged on the resin layer and that has a secondsurface that is in contact with the resin layer. In a section that isperpendicular to the second surface, an average flattening ratio of thefillers that are in contact with the second surface is larger than anaverage flattening ratio of the fillers that are not in contact with thesecond surface. Here, the flattening ratio is a ratio of a maximumlength of the filler in a direction parallel to the second surface to amaximum thickness of the filler in a direction perpendicular to thesecond surface.

A method of manufacturing an assembly of stacked elements according tothe invention comprises: a first element forming step to form a firstelement having a first surface; a resin layer forming step to form aresin layer on the first surface, wherein the resin layer contains aplurality of fillers; a grinding step to grind an upper surface of theresin layer; and a second element forming step to form a second elementon the upper surface of the resin layer that has been ground, whereinthe second element has a second surface that is in contact with theupper surface. Before the grinding step and after the resin layerforming step, a diameter of at least one of the fillers that arecontained in the resin layer is larger than a gap between the firstsurface and the second surface.

According to the present invention, it is possible to provide aconfiguration that can limit both the size of the assembly and the costof the fillers, as well as a method of manufacturing such an assembly.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description withreference to the accompanying drawings which illustrate examples of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are perspective views of a fan-out package;

FIGS. 2A and 2B are sectional views of the fan-out package shown inFIGS. 1A and 1B,

FIG. 3 is an enlarged view of portion B in FIG. 2B;

FIGS. 4A-4D are conceptual views illustrating fillers in various shapesbefore they are ground;

FIGS. 5A-5E are views illustrating the steps of a method ofmanufacturing the sensor package;

FIGS. 6A-6E are conceptual views illustrating fillers in various shapesafter they are ground;

FIG. 7 is a partial sectional view of a comparative example showing thesame portion as FIG. 3; and

FIG. 8 is a photograph of an example showing the same portion as FIG. 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An embodiment of the present invention will be described with referenceto the drawings. The present embodiment relates to a fan-out sensorpackage in which a sensor unit is connected to external connectionterminals via redistribution layers. However, the present invention isnot limited to such a sensor package, and may be applied to any assemblyof stacked elements having a first element; a filler containing resinlayer that is arranged on the first element; and a second element thatis arranged on the first resin layer. In the following descriptions, thedirection parallel to second surfaces 41 of redistribution layers 4 andin which redistribution layers 4 extend is referred to as X direction,the direction parallel to second surfaces 41 of redistribution layers 4and perpendicular to X direction is referred to as Y direction, and thedirection perpendicular to X and Y directions and perpendicular tosecond surfaces 41 of redistribution layers 4 are referred to as Zdirection. A section perpendicular to second surface 41 means anarbitrary section that is parallel to Z direction. It should be notedthat there are numerous numbers of sections that are perpendicular tosecond surface 41 and that such a section is not limited to the X-Zplane shown in the drawing. Similarly, there are numerous numbers ofdirections parallel to second surface 41, and such a direction is notlimited to X and Y directions.

FIGS. 1A and 1B show perspective views of sensor package 1. FIG. 1A is aperspective view illustrating the external shape of sensor package 1,and FIG. 1B shows a perspective view in which filler containing resin 6in FIG. 1A is omitted. Sensor package 1 includes sensor unit 2 thathouses a sensor element (not illustrated), extraction electrodes 3 thatare provided on a surface (first surface 21) of sensor unit 2,redistribution layers (conductive layers) 4 that are connected toextraction electrodes 3, respectively, and external connection terminals5 that are connected to redistribution layers 4, respectively. Sensorunit 2 houses a magnetic sensor using a TMR element, but the type of thesensor is not limited to this. For example, a Hall element or amagnetoresistive element, such as an AMR element and a GMR element, maybe used for the sensor. In the present embodiment, four extractionelectrodes 3, four redistribution layers 4 and four external connectionterminals 5 are provided, but the number is not limited to this. Minimumrectangle 8 that envelops four external connection terminals 5 alsoenvelops sensor unit 2, as seen in Z direction. In other words, sensorunit 2 is located inside minimum rectangle 8 that envelops four externalconnection terminals 5, as seen in the Z direction.

Sensor unit 2, extraction electrodes 3, redistribution layers 4 andexternal connection terminals 5 are sealed with filler containing resin6, except for the upper surface of external connection terminals 5 andbottom surface 22 of sensor unit 2. The resin that forms fillercontaining resin 6 is epoxy resin, but the type of the resin is notlimited to this. Other resins, such as phenol resin and polyimide resin,may also be used. The ratio of the fillers in the resin is not limitedand may be selected from the range between 10-90 mass percentage.

FIG. 2A is a sectional view of sensor package 1 taken along line A-A inFIG. 1B, and FIG. 2B is an enlarged view of portion A in FIG. 2A. Fillercontaining resin 6 includes first resin layer 61 that covers the sidesof sensor unit 2 and the sides of extraction electrodes 3, as well assecond resin layer 62 that covers the sides of redistribution layers 4and the sides of external connection terminals 5. In the presentembodiment, first resin layer 61 and second resin layer 62 have the sameconfiguration, including the diameter of the fillers, but may havedifferent configurations. Sensor unit 2 has a generally rectangularparallelepiped shape. Of six surfaces of sensor unit 2, the uppersurface that faces redistribution layers 4 forms first surface 21 thatis in contact with first resin layer 61. Bottom surface 22, which is theback surface of first surface 21, is exposed. Extraction electrodes 3that are formed of a conductive metal, such as Cu, are formed on firstsurface 21. Redistribution layers 4 are connected to extractionelectrodes 3 of sensor unit 2 after sensor unit 2 is formed.Redistribution layers 4 are formed of a conductive metal, such as Cu.Redistribution layers 4 extend substantially parallel to first surface21 of sensor unit 2 in a direction away from sensor unit 2. The surfaceof each redistribution layer 4 that faces sensor unit 2 forms secondsurface 41 that is in contact with first resin layer 61. Thus, gap 9whose dimension is equal to the space between first surface 21 andsecond surface 41 is formed between sensor unit 2 and redistributionlayers 4, and gap 9 is also filled with first resin layer 61. In otherwords, sensor unit 2 (the first element), first resin layer 61 andredistribution layers 4 (the second elements) form assembly 10 ofstacked elements. External connection terminals 5 are provided on theupper surfaces of respective redistribution layers 4. Externalconnection terminals 5 are formed of a conductive metal, such as Cu, Snand SnAg, and are electrically connected to redistribution layer 4,respectively.

FIG. 3 is an enlarged view of portion B in FIG. 2B illustrating asection that is perpendicular to second surface 41 of redistributionlayer 4 (the second element). Fillers F consist of various fillershaving different shapes and dimensions. For convenience, only fillersthat are spherical before they are ground are shown in FIG. 3, althoughthe shapes of some of the fillers are changed by grinding in the presentembodiment, as described later. FIGS. 4A to 4D are sectional viewsillustrating examples of various shapes of fillers F before the shapesare changed, that is, before the fillers are ground. FIG. 4A showsfiller F having a circular section, FIG. 4B shows filler F having asection of ellipse, and FIGS. 4C, 4D show fillers F having sections ofirregular shapes. In the present description, the maximum distancebetween two arbitrary points on the surface of filler F measured on astraight line is defined as the diameter of filler F. In other words,the diameter of filler F refers to the diameter of the sphere having thesmallest volume from among spheres that envelop filler F. For example,the diameter of spherical filler F is equal to the diameter of thesphere, and the diameter of ellipse-shaped filler F is equal to thelength of the major axis of the ellipse. For convenience, the diameterof the filler is shown as “d” in FIGS. 4A-4D. Thus, a plurality offillers F consists of fillers F having different filler diameters. Themaximum diameter of the fillers depends on the types of fillersavailable on the market.

Some of fillers F are in contact with first surface 21 (these fillers Fare referred to as first fillers F1), some of the other fillers F are incontact with second surface 41 (these fillers F are referred to assecond fillers F2), and the remaining fillers F are neither in contactwith first surface 21 nor in contact with second surface 41 (thesefillers F are referred to as third fillers F3). In the presentembodiment, in a section perpendicular to second surface 41, the ratioof maximum length L2 of each filler F in a direction parallel to secondsurface 41 to maximum thickness L1 of the same filler F in Z directionis defined as the flattening ratio. The average flattening ratio ofsecond fillers F2 is larger than the average flattening ratio of firstfillers F1 and third fillers F3, that is, the average flattening ratioof fillers F that are not in contact with second surface 41. In otherwords, second fillers F2 are more elongate in a direction parallel tosecond surface 41 than fillers F that are not in contact with secondsurface 41 on average. As described above, there are numerous numbers ofdirections that are parallel to second surface 41, and the directionsparallel to second surface 41 are not limited to X direction shown inthe figure. However, since fillers F are randomly oriented, the averageflattening ratio can be determined without major error by using anyavailable section. In addition, fine fillers having small diameters (forexample, diameter of less than 1 μm) may be excluded in determining theaverage flattening ratio. The shape of filler F will be described laterin more details.

Next, referring to FIGS. 5A-5E, a method of manufacturing sensor package1 according to the present embodiment will be described. First, as shownin FIG. 5A, a plurality of sensor units 2 is formed on support structure7 (first element forming step). Sensor units 2 may be formed on asilicon substrate in the wafer process. Alternatively, sensor units 2that are formed in the wafer process may be separated first, and may bethen bonded to a supporting tape by an adhesive. In the presentinvention, support structure 7 includes both a supporting substrate anda supporting tape. The interval between adjacent sensor units 2 isdetermined such that external connection terminals 5 of adjacent sensorunits 2 (formed in a subsequent step) do not interfere each other. Fourextraction electrodes 3 are formed on the upper surface of sensor unit2. Next, sensor units 2 are covered with first resin layer 61. Thus,first resin layer 61 that contains a plurality of fillers F is formed onthe first element (first resin layer forming step). First resin layer 61may be formed by compression or printing. First resin layer 61 coversnot only sensor unit 2 but also extraction electrodes 3. Thereafter,first resin layer 61 is cured. The maximum thickness of at least onesecond filler F2 that is contained in first resin layer 61, measured inZ direction, or the maximum diameter of the fillers, is larger thandimension H of gap 9 between sensor unit 2 (the first element) andredistribution layer 4 (the second element), which will be formed in asubsequent step. Thus, when dimension H of gap 9 is, for example, about30 μm, the maximum diameter of the fillers may be, for example, equal toor more than 50 μm.

Next, as shown in FIG. 5B, the upper surface of first resin layer 61that has cured is ground (grinding step). The grinding step may becarried out, for example, by mechanical grinding, by CMP (ChemicalMechanical Polishing) or by a combination of mechanical grinding andCMP. First resin layer 61 and extraction electrodes 3 are ground untilextraction electrodes 3 are exposed and the thickness of extractionelectrodes 3 is reduced to less than the maximum thickness of secondfiller F2. Thus, some of second fillers F2 that are contained betweenthe upper surface of first resin layer 61 that is present before thegrinding step and the upper surface of first resin layer 61 that ispresent after the grinding step are entirely or partially removed. Mostof second fillers F2 that are exposed on the upper surface of firstresin layer 61 after the grinding step are made flat on the uppersurface.

FIGS. 6A-6E conceptually show various shapes of second fillers F2 aftergrinding. The resin that has been cured is not largely deformed bygrinding. Fillers F stay substantially at the same positions, and theupper portions of fillers F are removed and made flat by grinding. Ifthe original shape of filler F is, for example, spherical, then filler Fis deformed into a sphere with the upper portion removed, as shown inFIG. 6A. If the original shape of filler F is, for example, an ellipse,then filler F is deformed into an ellipse with the upper portionremoved, as shown in FIG. 6B. Some of fillers F are in surface contactwith second surface 41, as shown, for example, in FIGS. 6A-6E. Some offillers F have the maximum length on second surface 41 in a directionparallel to second surface 41, as shown, for example, in FIGS. 6A, 6Cand 6E. Some of fillers F extend flatly along second surface 41, asshown, for example, in FIGS. 6A-6D. Some of fillers F have whisker 13that extends on second surface 41 at the end of the filler that is incontact with second surface 41, as shown, for example, in FIG. 6C.Whisker 13 is considered to be generated by a grinding pad pullingfiller F during the mechanical grinding. Some of fillers F have notch 11at the end of the fillers, as shown, for example, in FIG. 6D. Notch 11is considered to be generated by a grinding pad pushing filler F duringthe mechanical grinding. Some of fillers F form cavity 12 between thefillers and second surface 41, as shown, for example, in FIG. 6E. Cavity12 is considered to be generated by a grinding pad pushing both ends offiller F during the mechanical grinding. As described above, fillers Fhave various shapes, but the shapes shown FIGS. 6A-6E are not ones thatthe fillers normally have, and these shapes are considered to begenerated by grinding.

Next, as shown in FIG. 5C, redistribution layers 4 (the second elements)are formed on the upper surface of first resin layer 61 that has beenground (second element forming step). The lower surfaces ofredistribution layers 4 (second surface 41) are in contact with theupper surface of first resin layer 61 that has been ground.Redistribution layers 4 are connected to extraction electrodes 3.Redistribution layers 4 are formed, for example, by plating, sputtering,printing and coating. Next, external connection terminals 5 are formedon redistribution layers 4. External connection terminals 5 are formed,for example, by plating, sputtering, printing and coating. Next, asshown in FIG. 5D, redistribution layers 4 and external connectionterminals 5 are sealed with second resin layer 62. A filler containingresin may be used as second resin layer 62, like first resin layer 61.Next, as shown in FIG. 5E, second resin layer 62 is ground untilexternal connection terminals 5 are exposed. Thereafter, each sensorpackage 1 is separated, and support structure 7 is removed. Supportstructure 7 is removed in the present embodiment, but may be used aspart of the product.

FIG. 7 is a sectional view of a conventional sensor package showing thesame portion as FIG. 3. The maximum filler diameter of first resin layer61 is smaller than the maximum filler diameter of first resin layer 61of the present embodiment. The diameters of fillers F that are presentbetween sensor unit 2 and redistribution layers 4 are smaller thandimension H of gap 9, and fillers F are substantially spherical.However, fillers having a small maximum diameter are costlier thanfillers having a large maximum diameter. In the present embodiment, thecost of sealing resin can be reduced because fillers having a largemaximum diameter can be used.

In addition, in the present embodiment, first resin layer 61 ischaracterized by good heat dissipation capability. First resin layer 61requires good thermal conductivity in order to dissipate heat that isgenerated in sensor unit 2. The thermal conductivity of first resinlayer 61 largely depends on the thermal conductivity of the fillersbecause, in general, the thermal conductivity of resin is low and thethermal conductivity of fillers is high. For example, the thermalconductivity of SiO₂, which is an example of the material of the filler,is about 8 Wm⁻¹K⁻¹, while the thermal conductivity of epoxy resin is assmall as about 0.21 Wm⁻¹K⁻¹. In the present embodiment, due to thefillers having a large maximum diameter, a large contact area betweenfillers F and redistribution layers 4 (to be more precise, contact areabetween redistribution layers 4 and filler F per unit area ofredistribution layer 4) can be easily ensured. This enhances heatconductivity from redistribution layers 4 to fillers F. In addition, thenumber of boundaries between fillers F and the resin decreases in firstresin layer 61. Thus, heat that is generated in sensor unit 2 is easilytransferred to redistribution layers 4 via a limited number of fillers Fso that heat transfer paths can be easily ensured in first resin layer61. In other words, heat transfer paths are less likely to be cut by theresin and heat that is generated in sensor unit 2 can be moreefficiently transferred to redistribution layers 4. It should be notedthat the thermal conductivity of resin layer 6 is improved as a whole inthe present embodiment because fillers F having a large maximum diameterare also used in portions other than gap 9.

In addition, since fillers having small diameters easily move while theyare ground, small unevenness tends to occur on the surface that has beenground, and the small unevenness may lead to cavities between firstresin layer 61 and redistribution layers 4. In the present embodiment,due to the use of fillers having a large maximum diameter, the number offillers of small diameters relatively decreases, and the surface offirst resin layer 61 that has been ground tends to be made flat.

FIG. 8 is a photograph of sensor package 1 that has been manufacturedaccording to the present embodiment, showing the same portion as FIG. 3(for convenience, elements other than the resin layer are conceptuallyillustrated). In the figure, the black parts show epoxy resin and thewhite parts show fillers F. Dimension H of the gap is 18 μm, and themaximum diameter of the fillers is 25 μm. As described above, firstresin layer 61 contains various kinds of fillers F that are different inshape and dimension. It is confirmed from FIG. 8 that fillers F that arein contact with redistribution layers 4 in gap 9 between sensor unit 2and redistribution layers 4 have been made flat by mechanical grinding.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made without departing from the spiritor scope of the appended claims.

LIST OF REFERENCE NUMERALS

-   -   1 sensor package    -   2 first element (sensor unit)    -   21 first surface    -   3 extraction electrode    -   4 second element (redistribution layer)    -   41 second surface    -   5 external connection terminal    -   6 resin layer    -   61 first resin layer    -   10 assembly of stacked elements    -   F filler    -   F1 first filler    -   F2 second filler    -   F3 third filler

What is claimed is:
 1. An assembly of stacked elements comprising: afirst element having a first surface; a resin layer that is arranged onthe first surface and that contains a plurality of fillers; and a secondelement that is arranged on the resin layer and that has a secondsurface that is in contact with the resin layer, wherein, in a sectionthat is perpendicular to the second surface, an average flattening ratioof the fillers that are in contact with the second surface is largerthan an average flattening ratio of the fillers that are not in contactwith the second surface, wherein the flattening ratio is a ratio of amaximum length of the filler in a direction parallel to the secondsurface to a maximum thickness of the filler in a directionperpendicular to the second surface.
 2. The assembly of stacked elementsaccording to claim 1, wherein at least one of the fillers that are incontact with the second surface is in surface contact with the secondsurface.
 3. The assembly of stacked elements according to claim 1,wherein at least one of the fillers that are in contact with the secondsurface has the maximum length on the second surface.
 4. The assembly ofstacked elements according to claim 1, wherein at least one of thefillers that are in contact with the second surface extends flatly alongthe second surface.
 5. The assembly of stacked elements according toclaim 1, wherein at least one of the fillers that are in contact withthe second surface has a whisker that extends on the second surface atan end of the filler.
 6. The assembly of stacked elements according toclaim 1, wherein at least one of the fillers that are in contact withthe second surface has a notch at an end of the filler.
 7. The assemblyof stacked elements according to claim 1, wherein at least one of thefillers that are in contact with the second surface forms a cavitybetween the second surface and the filler.
 8. The assembly of stackedelements according to claim 1, wherein a surface of the resin layer thatis in contact with the second surface is ground.
 9. A sensor packagecomprising the assembly of stacked elements according to claim 1,wherein the first element is a sensor unit, the second element is aconductive layer, further comprising an extraction electrode thatconnects the sensor unit to the conductive layer, wherein the extractionelectrode and the resin layer are provided between the sensor unit andthe conductive layer.
 10. The sensor package according to claim 9,wherein more than one of the extraction electrodes are connected to thesensor unit, and more than one of the conductive layers are connected tothe extraction electrodes, respectively, further comprising externalconnection terminals that are connected to the conductive layers,respectively, and a minimum rectangle that envelops the externalconnection terminals envelops the sensor unit, as seen in a directionperpendicular to the second surface.
 11. A method of manufacturing anassembly of stacked elements comprising: a first element forming step toform a first element having a first surface; a resin layer forming stepto form a resin layer on the first surface, wherein the resin layercontains a plurality of fillers; a grinding step to grind an uppersurface of the resin layer; and a second element forming step to form asecond element on the upper surface of the resin layer that has beenground, wherein the second element has a second surface that is incontact with the upper surface, wherein, before the grinding step andafter the resin layer forming step, a diameter of at least one of thefillers that are contained in the resin layer is larger than a gapbetween the first surface and the second surface.
 12. The methodaccording to claim 11, wherein some of the fillers that are containedbetween the upper surface of the resin layer that is present before thegrinding step and the upper surface of the resin layer that is presentafter the grinding step are entirely or partially removed in thegrinding step.
 13. The method according to claim 11, wherein the fillerthat is exposed on the upper surface of the resin layer after thegrinding step is made flat on the upper surface.
 14. The methodaccording to claim 11, wherein the grinding step is carried out bymechanical grinding.
 15. The method according to claim 11, wherein amaximum diameter of the fillers is equal to or more than 50 μm.
 16. Amethod of manufacturing a sensor package comprising the method accordingto claim 11, wherein in the first element forming step, a sensor unit isformed as the first element, wherein the sensor unit has an extractionelectrode formed on an upper surface thereof; in the resin layer formingstep, the sensor unit and the extraction electrode are sealed with theresin layer; in the grinding step, the resin layer and the extractionelectrode are ground until a thickness of the extraction electrode isreduced to less than a maximum thickness of the fillers; in the secondelement forming step, a conductive layer is formed as the secondelement, wherein the conductive layer is connected to the extractionelectrode; and after the second element forming step, an externalconnection terminal is formed on the conductive layer.